1. FIeld of the Invention
This invention relates to a prosthesis for the living body used for restoring the missing function and hard tissue in the living body brought about by diseases and accidents and to a method of making the same.
2. Prior Art
When people are deprived of the articular function of their limbs by a disease such as rheumatold arthritis which predilectly attacks women of 20 to 40 years of age, an operation for replacing the lost function of the joint by an artificial bone is often performed as one of surgical therapeutic methods in addition to pharmaceutical therapy, and is conducted mostly in the treatment of hip joints and knee joints.
Presently, artificial joints are mostly made of metal and plastic as a raw material and are extensively used in an artificial hip joint, knee joint, shoulder joint, finger joint and the like. The greatest problem common to those artificial joints lies in loosening (i.e. getting loosened during use). Namely, several years after an artificial joint replacement operation, there occurs a loosening between the joint and the bone and the loosening causes pain and reduction in the function of artificial joint with the result that there are not a few instances wherein removal of the artificial joint and reoperation must be performed.
In an artificial joint replacement operation, an acrylic resin referred to as bone cement is used during the operation in order to bond the artificial joint to the epiphysis of bone but the use of the bone cement involves following disadvantages (1) that because the resin generates a heat of 70.degree. to 80.degree. C. when it is polymerized and solidified, such heat of polymerization solidifies protein of the bone and soft tissue to bring them into necrosis, (2) that the monomer left during polymerization also has toxicity, From the disadvantages in (1) and (2), it may result that although the use of the bone cement provides firm bonding between the necessary portions of the bone in a shortened period of operation, the cement constitutes one factor in the loosening of the bone portion in a later day. Furthermore, in the case of a metallic artificial joint, it is hard to prevent corrosion of the metal material in the human body and there is a danger of metallic ions producing harmful effects on the body to bring the living body into necrosis.
From this point of view, an alumina ceramic artificial joint has been developed which is free from corrosion in the body and can be conglutinated into one body with the bone without the use of bone cement because of its excellent biocompatibility with the bone, and has widely been used in many joints of the human body such as knee joint, foot joint. However, the alumina ceramics is excellent in stability and high in mechanical strength in the living body, while because it is an inert material, it takes a considerably long period of time before it comes to conglutinate with a natural bone and is solidified after implantation, if the ceramic surface is smooth. Accordingly, in order to promote conglutination of the artificial joint with the bone, the art of forming large and small grooves on the surface of the alumina artificial joint was proposed. The grooves are effective for the prevention of lateral slip of the artificial joint and for fixing the artificial joint in proper position to the bone, but are liable to be short in anchoring effect (catching effect) in the direction of vertical tension with respect to the bone surface, and then it takes a long time to fix the artificial joint to the bone with the aid of the grooves in contrast to bonding time by use of bone cement. This is a problem concerning an artificial joint of alumina ceramics.